>>717819197Developmental biology is all about producing weird congenital failures in order to better understand how shit works.
Like for example there is a gene called sonic hedgehog that plays a part in digit development, so if you have a defect in that gene you might come out with missing or malformed fingers and hands.
And in this case they seem to have knocked out the genes responsible for growing appendages.
And in fruit flies for example they managed to make legs grow instead of antennae.